The second order Doubly Asymptotic Approximation (DAA2) method, has been implemented in the SWEEPS-STAGS code to provide a steady-state vibration analysis capability for submerged structures. This paper extends the previous work in determining the convergence behavior of DAA2-predicted wet surface variables. The convergence rates of fluid boundary eigenvalues and convergence behaviors of modal acoustic impedance functions are calculated for increasingly dense fluid element grids on a spherical surface. Within mode-dependent frequency ranges in which DAA2 is valid, dense grids on the order of five elements per half-wave are needed for five percent accuracy in modal acoustic impedance. This is a consequence of the low order (constant source strength) interpolation used for establishing fluid variables. There are mode-dependent frequency ranges for which DAA2 acoustic impedance predictions are inaccurate, even for very dense developing SWEEPS-STAGS idealizations for vibrations analysis of complex submerged structures.